This invention relates generally to heat exchangers and, more particularly, to microchannel heat exchangers for use in air conditioning and refrigeration vapor compression systems.
Refrigerant vapor compression systems are well known in the art and are commonly used for conditioning air to be supplied to a climate controlled comfort zone within a residence, office building, hospital, school, restaurant, or other facility. A conventional refrigerant vapor compression system 20, as illustrated in FIG. 1, typically includes a compressor 22, a condenser (or gas cooler) 24, an expansion device 26, and an evaporator 28 interconnected by refrigerant lines to form a closed refrigerant circuit. As refrigerant flows through the expansion device 26, the pressure of the refrigerant decreases such that typically 10-20% of the refrigerant vaporizes. If the flash gas or vaporized refrigerant circulates through the evaporator 28 with the liquid refrigerant, the pressure drop in the evaporator 28 increases, thereby decreasing the performance of the vapor compression system 10. In addition, the flow of flash gas through the evaporator 28 results in maldistribution of the refrigerant among the multiple conduits in the evaporator 28, leading to less than optimal utilization of the heat transfer surface thereof.
To maximize the efficiency of the refrigerant vapor system, an external separator is fluidly connected to the closed loop refrigeration circuit downstream from the expansion valve and upstream from the evaporator. The separator divides the 2-phase refrigerant mixture from the expansion device into liquid refrigerant and vaporized refrigerant. The liquid refrigerant is provided to the evaporator, and the flash gas is provided directly to an inlet of the compressor. Bypassing the flash gas around the evaporator can result in capacity and coefficient of performance (COP) improvements of about 20%. The additional components and controls associated with integrating an external separator into the vapor compression system, however, increase both the cost and complexity of the system, essentially nullifying any benefits achieved and making application of an external separator typically impractical.